1620s, from French lilac "shrub of genus Syringa with mauve flowers," from Spanish lilac, from Arabic lilak, from Persian lilak, variant of nilak "bluish," from nil "indigo" (compare Sanskrit nilah "dark blue"), of uncertain origin. As a color name, attested from 1791; as a scent, from 1895. As an adjective, "pale pinkish-purple," from 1801. Related: Lilaceous.